Sterilization of surgical dressings



June 17, 1958 w. L. GEORGE sTERILIzATIoN oF SURGICAL DRESSINGS Filed May8, 1956 vl .mmndlw lullunh.. .lllilllliif!! Illlllllllll INVENTOR MUA/w$504965.

ATTORNEY United States lPatent O STERILIZATION F SURGICAL DRESSINGSWilliam L. George, Middlesex, N. J., assignor to Johnson & Johnson, acorporation of New Jersey Application May 8, 1956, Serial No. 583,529

3 Claims. (Cl. 21--58) This invention relates to sterilization offibrous materials with vapors of water and formaldehyde, and moreparticularly to a method of applying the sterilizing agent in'the formof a liquid under critical conditions to avoid deterioration of thefibrous materials, and is a continuation-inpart of my previousapplication Serial No. 266,201, filed Jan. 12, 1952, now abandoned.

Sterilization by means of vapor of water and formaldehyde is well knownand has achieved considerable cornmerical success. One method forcarrying it out is by introducing the material to be `sterilized in anautoclave or the like vessel. If the material to be sterilized isprewrapped, the wrapping must be porous. From the cornmercial viewpoint,this method is undesirable since it is carried out in a batch fashionand is relatively slow and cumbersome. The art is confronted by theproblem of providing an economic and convenient method for applyingthese sterilizing agents to wrapped brous materials, especially to suchmaterial having desirable loft which loft is susceptible todeterioration upon prolonged wetting with aqueous liquid.

The discoveries associated with the invention relating to solution ofthe above problems, and the objects achieved in accordance with theinvention as set forth herein include: a provision of the process forsterilizing a fibrous surgical dressing by treatment with vapors ofwater and formaldehyde in a wrapping which is bacteria impermeable butpermeable to said vapors, which dressing is susceptible to undesirableloss of loft upon prolonged wetting with an aqueous liquid, in whichprocess the sterilizing material is applied to the fibrous material asaqueous formaldehyde liquid'in an amount and concentra tion to provideformaldehyde in an amount :and a range of 0.4 to 1.5% based on theweight of the dressing plus the wrapping and water in an amount in therange of 3 to 10% based on the weight of the dressing, then wrapping thedressing within one sec. to 3 min. in the abovementioned wrappingmaterial, and maintaining it at a temperature in the range of 50 to 200F. and a moisture content in the range of 3 to 10% for a time in therange of l hour to 3 weeks; the provision of such a process using aformaldehyde concentration range of 0.48 to 1.0% and a temperature rangeof 50 to 170 F. the provision of such a process using formaldehydeconcentration range of 0.6 to 1.0%, a water concentration of 4.8% andthe temperature range of 100 to 150 F.; and other objects which will beapparent as details or'embodiments of the invention as set forthhereinafter.

The invention will be described by reference to the accompanyingdrawing, in which Fig. 1 is in the nature of a flow diagram and Fig. 2is a `vertical section taken through the portion of the equipment inwhich ythe concentrated aqueous formaldehyde solution is applied to thedressing.

Referring for the present to Fig. l, number representsa storage vesselinto which the aqueous formaldehyde solution is introduced through pipe11, control valve `12, arid strainer 15. Pipe and valve 16 may be usedto ICC 2 drain tank 10 when this is desired. The solution ows throughpipe 17, control valve 18, and filter 20, and through rotameter 21 orother suitable apparatus for measuring and controlling flow of liquidmaterial at a very low rate. Constant displacement pump 22 forcessolution through pipe 25 into nozzle 26, which is illustrated on alarger scale in Fig. 2. The aqueous formaldehyde solution emerges fromnozzle 26 at tip 27,`.at` which point the liquid is in the form of adroplet above the tip. 30 represents a horizontal track which carriesand on which is supported a surgical dressing, such as Hadhesivebandage31. A portion of continuous belt or chain is indicated at 32, whichbel-t is moving in a horizontal direction from left to right. Belt 32carries a lug 35 which urges bandage 31 along its path on top of track30. t

Bandage 31 is formed from the usual backing strip and adhesive layer 36,having secured thereto a surgical.

dressing 37, having high loft. A pair `of overlapping protective stripsmade, for example, of crinoline, are shown at 40.

Just after the aforementioned droplet disposed on the top of tip 27 isformed, bandage 31 moves over the tip in its path from left to right,contacts this droplet and removes it from the tip. Within a relativelyshort period of time, the solution becomes dispersed through thedressing. rThe bandage passes immediately to wrapping and sealing meansshown diagrammatically at 41, where it is wrapped and preferably sealedin paper such as glassine or other low porosity super-calendered paper.The wrapped dressings arethereafter assembled in packages at 42, thepackages are transferred to suitable conditioning zone 43, where theaqueous formaldehyde treated and wrapped bandages are maintained at asuitable temperature for time to accomplish sterilization.

By controlling the rate of ow of aqueous formaldehyde solution throughnozzle 26, the concentration yof formaldehyde in the solution, and thenumber of dressings passing tip 27 per minute, the amount offormaldehyde as HCHO introduced per dressing is maintained above about0.4 percent by weight based on the dressing plus the wrapping material.

In order to facilitate a clear understanding `of the in vention, thefollowing preferred specific embodiments are described in detail.

t Example 1 Aqueous formaldehyde solution containing 20 percent HCH() ispassed from storage tank 10 through pipe 17, rotameter 21, pump 22 andpipe 25 into nozzle 26 at a rate controlled, in conjunction with thefrequency `at which adhesive bandages 31 are manufactured and passedover tip 27, so that each bandage, weighing on the average, about 0.4gms., including the Wrapper, absorb about 0.003 to 0.0035 parts of HCHO.The bandages are formed from a fabric adhesive-coated backing, in theadhesive a surgical dressing made up of nonwoven cotton or rayon fiberswrapped in a gauze and having high loft, and overlapped layers ofcrinoline (or if desired, smooth facing material) protecting theadhesive and the pad. The aqueous formaldehyde is applied to thecrinoline side of the bandage. After treatment, the adhesive bandage. iswrapped and sealed in about l to 3 seconds in low porositysuper-calendered glassine paper.` Twenty samples are analyzedindividually fori-ICHO, taken immediately after wrapping, one aboutevery hour over a period of operation of one day. The HCH() content ofthe bandages ranges from 0.73% to 0.96%, based on bandage plus wrapper.The moisture content of the wrapped bandages is about 61/2% based on thebandage alone and exclusive of wrapper. A total of about 300 bandages,`taken at uniform time intervals throughout 3 the day are. marked forsterility tests, but processed with the other bandages. The individuallywrapped bandages are placed in cartons, about 4,000 per carton. Thecarton is then placed in a conditioning zoney maintained at 120' F. forl5y hours. After conditioning for a total of 15 hours, theabove-mentioned marked bandages are eXa-minedand found to be sterile (U.S. Pharmacopoeia method).

Example 2 Adhesive bandages of the above type are inoculated with thefollowing:

Bacillus subtilis Clostridium sporogenes Eschirichia. coli.

Staphylococcus aureus Staccharomyces cerivsiae Aspergillus niger Anotherspecies of Aspergillus mold having known high resistance to HCHO Thesecontaminated adhesive bandages are then treated With aqueousformaldehyde solution containing 17.7% HCHO on the apparatus and in themanner described in Example 1.. The relative humidity of the air duringaqueous formaldehyde treatment and wrapping is 60%. 0.5% HCHOis added toeach bandage (based on the weight of bandage plus wrapper), 2.2% water(based on bandage, exclusive of wrapping) is added in the aqueousformaldehyde solution, and the total moisture content of the wrappedbandage is 5.7%. The wrapped bandages packaged as described in Example 1are conditioned at 110 F. for 15 hours. The conditioned bandages arethen examined and found to be sterile.

Example 3 Adhesive bandages of the above type are inoculated withbacteria. These contaminated adhesive bandages are then treated withaqueous formaldehyde solution containing 10.0% HCHO on the apparatus andin the manner described in Example l. The relative humidity of the airduring aqueous formaldehyde treatmentl and wrapping is 75%. 0.48% HCHOis added to each bandage (based on the weight of bandage plus wrapper).4.2% water is added in the aqueous formaldehyde solution, and the totalmoisture content of the wrapped bandage (based on bandage alone) was8.3%. The wrapped bandages, packaged as described in Example 1, areconditioned at 140 F. for 1 hour. The conditioned bandages are thenexamined and found to be sterile.

Example 4 Adhesive bandages of the above type are inoculated withbacteria. These contaminated adhesive bandages are then treated withaqueous formaldehyde solution containing 10.0 percent HCHO ontheapparatus and in the manner described in Example l. 0.48 percent HCHOis added to each bandage (based on the weight of bandage plus wrapper).4.2 percent water is added in the aqueous formaldehyde solution, and thetotal moisture content of the wrapped bandage (based on bandage alone)is 7.5 percent. The wrapped bandages, packaged as described in Example1, are conditioned at 160 to 170 F. for 1 hour. The conditioned bandagesare then examined and found to be sterile.

Example 5 Adhesive bandages` of the type described in Example l areinoculated withvthe bacteria specied in Example 2. These contaminatedadhesive bandages are then treated withl aqueous formaldehyde solutioncontaining 20 percent HCHO, 32 percent methyl alcohol, and 48 percentwater, on the apparatus and in the manner described in Example 1. Therelative humidity of the air during aqueous formaldehyde treatment andwrapping is 38 percent. 0.48 percenty HCHO is added to each bandage(based on the 4 weight of bandage plusI wrapper. 1.0v percent, water is`added in the aqueous formaldehyde solution, and the total moisturecontent of the wrapped bandage (based on bandage alone) is 3.1 percent.The wrapped bandages, packaged as described in Example 1, areconditioned at 70 F. in 2O percent R. H. ambient air for 2 weeks. Theconditioned bandages are then examined and found to be sterile.

Example 6 Adhesive bandages of the type described in Example 1 areinoculated with the bacteria specified in Example 2. These contaminatedadhesive bandages are then treated with aqueous formaldehyde solutioncontaining 17.7 percent HCHO on the apparatus andr in the mannerdescribed in Example 1. The relative humidity of the air during aqueousformaldehyde treatment and wrapping is 38 percent. 0.48 percent HCHO isadded to each bandage (based on the weight of bandage plus wrapper). 2.2percent water is added in the aqueous formaldehyde solution, and the`total moisture content of the wrapped bandage (based on bandage alone)is 4.3 percent. The wrapped bandages packaged as described in Example lare conditioned at '70 E. in 20 percent R. H. ambient air for 2 Weeks.The conditioned bandages are then examined and found to be sterile.

Comparable results to the foregoing may be achieved with the variousmodifications thereof including the following. The formaldehydeconcentration should be in the range of 0.4 to 1.5%, desirably 0.48 to1% andy prefer ably 0.6 to 1%, based on the weight of the dressing pluslthe Wrapping, and the water concentration in the range of 3 to 10% basedon the weight of the dressing. Lower contentsof formaldehyde do not giveadequate or reliable sterilization. Higher amounts are generally notnecessary for the sterilization, and may give rise to undesirable odorproblems. In addition, the higher contents of formaldehyde are avoidedfor economic reasons. Lower contents of water do not give adequate orreliable sterilization; and higher or excessive amounts are to beavoided in order to avoid undesirable deterioration of the loft orabsorbency of the dressing.

The Water may be introduced with the formaldehyde desirably as aqueousformaldehyde above about 8% by' weight formaldehyde concentration, andpreferably about 37%. The treated dressing may contain some moisture,and in such case, only the needed additional amount is added. Therelative humidity of the atmosphere surrounding the wrapped bandages maybe controlled to regulate the moisture content within the desired range,i. e., 3 to 10%. A desirable relative humidity is above about 20%.

The temperature of the wrapped materials is maintained in the range ofabout 50 to 200 F., desirably 50 to 170 and preferably 100 to 150 F. Thebandages are maintained at this temperature for a time in the range ofabout 1 hour to three weeks, the higher temperatures requiring theshorter times for adequate sterilization, and vice versa.

As the term is used herein, aqueous solutions are intended to cover allsolutions containing water. Preferably, the aqueous solvent for the HCHOcontains a major proportion, i. e. 50% or more, water. However, in cer-`tain instances, it may be desirable to replace more of the water of theaqueous formaldehyde with alcohol or other non-aqueous solvent, forexample, to reduce bleeding of mercurochrome dressings orl dressingstreated with similar Water soluble medicaments. According to thisernbodi`- ment, which is within the scope of the invention, watercontent of the solvent (exclusive of HCHO solute) may be reduced to notless than about 15% by weight, the remaining being non-aqueous solvent.

The wrapped and packaged individual dressings which, of course, havebeen treated with the aqueous formalde hyde are preferably assembled ina relatively/'large number in a large size carton during conditioning.This affords not only efficiency of space utilization in the factory,but also facilitates handling problems since the bandages may besterilized in the pacakages in which they are distributed and sold.Formaldehyde tends to adhere to the dressing and hence the inventionmethod enjoys the prolonged sterilizing effect of the residualformaldehyde remaining in the wrapped bandage.

The bacteria impermeable wrapping which is permeable to the sterilizingvapors may be glassine or the like super-calendered paper or it may beof other material including known micro-porous plastic materials. Theinvention is applicable to so-called round or surgical Sponges, cottontips, and similar materials made up of fibrous material, each of whichhas desirable loft and absorbency, which properties are susceptible toundesirable loss or deterioration upon prolonged wetting with an aqueousliquid.

The aqueous formaldehyde may be applied to the bandages or othermaterials at any point in their manufacture, preferably, however, it isapplied just before the wrapping. The time lack between application ofthe aqueous formaldehyde and the wrapping should be within the range ofabout 1 sec. to 3 min. Further, the apparatus described in Figs. 1 and 2is but one illustration of means for contacting the aqueous formaldehydesolution with the dressing, which means is subject to variation. Forexample, instead of applying the solution on the bottom of the dressing,it may be sprayed or otherwise introduced onto the top of the dressing,either before or after the continuous strip of Process material issevered into individual bandages.

In view of the foregoing disclosures, variations or modificationsthereof will be apparent, and it is intended to include within theinvention all such variations and modications except as do not comewithin the scope of the appended claims.

I claim:

1. In the method of sterlizing a fibrous surgical dressing by treatmentwith vapors. of water and formaldehyde in a wrapping which isbacteria-impermeable but permeable to said vapors, which dressing issusceptible to undesirable loss of loft upon prolonged wetting with anaqueous liquid, the improvement which comprises providing in saiddressing aqueous formaldehyde liquid in an amount and concentration toprovide formaldehyde in an amount in the range of 0.4 to 1.5% based onthe weight of the dressing plus the wrapping, and water in an amount inthe range of 3 to 10% based on the weight of the dressing, wrapping thesaid dressing within l sec. to 3 min. and maintaining at a temperaturein the range of 50 to 200 F. at a moisture content within the said rangeof 3 to 10% for a time in the range of one hour to 3 weeks, wherebythere is obtained a non-deteriorated fibrous surgical dressing which issterile and individually wrapped in bacteria-impermeable material.

2. The method of claim 1 wherein the formaldehyde concentration is inthe range of 0.48 to 1.0% and the temperature is in the range of 50 to170 F.

3. The method of claim 2 wherein the formaldehyde concentration range is6.0 to 1.0%, the water concentration range is 4 to 8% and thetemperature range is 100 to 150 F.

References Cited in the tile of this patent UNITED STATES PATENTS2,075,845 Gross Apr. 6, 1937 2,329,928 Mulligan Sept. 1, 1943 2,386,157Barthen Oct. 2, 1945 FOREIGN PATENTS 623,733 Great Britain May 23, 1949972,908 Great Britain Sept. 6, 1950

1. IN THE METHOD OF STERILIZING A FIBROUS SURGICAL DRESSING BY TREATMENTWITH VAPORS OF WATER AND FORMALDEHYDE IN A WRAPPING WHICH ISBACTERIA-IMPERMEABLE BUT PERMEABLE TO SAID VAPORS, WHICH DRESSING ISSUSCEPTIBLE TO UNDESIRABLE LOSS OF LOFT UPON PROLONGED WETTING WITH ANAQUEOUS LIQUID THE IMPROVEMENT WHICH COMPRISES PROVIDING IN SAIDDRESSING AQUEOUS FORMALDEHYDE LIQUID IN AN AMOUNT AND CONCENTRATION TOPROVIDE FORMALDEHYDE IN AN AMOUNT IN THE RANGE OF 0.4 TO 1.5% BASED ONTHE WEIGHT OF THE DRESSING PLUS THE WRAPPING, AND WATER IN AN AMOUNT INTHE RANGE OF 3 TO 10% BASED ON THE WEIGHT OF THE DRESSING, WRAPPING THESAID DRESSING WITHIN 1 SECTO 3 MIN. AND MAINTAINING AT A TEMPERATURE INTHE RANGE OF 50 TO 200*F. AT A MOISTURE CONTENT WITHIN THE SAID RANGE OF3 TO 10% FOR A TIME IN THE RANGE OF ONE HOUR TO 3 WEEKS, WHEREBY THEREIS OBTAINED A NON-DETERIORATED FIBROUS SURGICAL DRESSING WHICH ISSTERILE AND INDIVIDUALLY WRAPPED IN BACTERIA-IMPERMEABLE MATERIAL.